266 



On the Nervous Circle which connects the voluntary Muscles with the 

 Brain. By Charles Bell, Esq. Communicated by the President, 

 January 25, 1826. Read February 16, 1826. [Phil. Trans. 1826, 

 Part II. p. 163.] 



The author's object in this communication is to show that every 

 muscle is supplied with two nerves of different properties, and that 

 where nerves of different functions have a separate origin, and run a 

 different course, two nerves must unite in the muscle in order to 

 perfect the relation betwixt the brain and those muscles. 



Referring to his former observations, Mr. Bell remarks, that when 

 he had distinguished two classes of nerves going to the face, and had 

 deprived the muscles of motion by dividing the nerve, a question na- 

 turally suggested itself as to the use of the remaining nerves, more 

 especially on finding that the 5th pair, or sensitive nerve, was more 

 profusely distributed to the muscles than to the skin, although they 

 are found in surgical operations by no means to possess that exqui- 

 site sensibility which such abundance of nerves would appear to in- 

 dicate. 



The lower maxillary nerve, which is a branch of the fifth pair, is 

 composed of a nerve of sensation and a nerve of motion, arising in 

 two sorts, one the sensitive, the other the muscular. On the former 

 division the Gasserian ganglion is formed, but the motive nerve may 

 be traced clear of the ganglion to the muscles of the jaws. Now if 

 all that is necessary to the action of a muscle be a nerve to excite 

 contraction, these branches, says the author, should have been un- 

 accompanied ; but, on the contrary, they are joined before they enter 

 the muscles by the sensitive nerves of the ganglion. 



These and similar facts and observations lead Mr. Bell to ask why 

 nerves of sensation are thus profusely given in addition to their mo- 

 tive nerves ; and in the progress of this inquiry, he shows that a 

 consciousness of the state and degree of action of the muscles is ne- 

 cessary to the governance of the muscular frame ; that motive nerves 

 are not those by which such information is conveyed to the brain, 

 for they are concerned in carrying the influence of the will to the 

 muscle ; and it is not likely that the same nerve should be active in 

 two directions at the same moment ; for, without reference to the 

 cause, a simple nerve has the influence propagated along it in one 

 direction only, and cannot be shown to act both from and to the 

 sensorium, as may be proved by actual experience, and in illustration 

 of which, Mr. Bell refers to the effects of sundry nerves, and to cer- 

 tain cases of their morbid affections. 



The author, therefore, concludes that between the brain and mus- 

 cles there is a circle of nerves, that one nerve conveys the influence 

 of the brain to the muscle, and that another gives the sense of the 

 condition of the muscle to the brain. If this circle be broken by the 

 division of the motive nerve, motion ceases ; if it be broken by the 

 division of the other nerve, there is no longer a sense of the condition 

 of the muscle, and therefore no regulation of it actively. 



